凯旋门

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正月初三，寓于巴黎，是日驾马车至凯旋门下，环岛盘桓。大道十二，辐辏如星；车流纵横，无灯无界。昔汤姆·克鲁斯拍碟中谍6于此地：飞车逐影，惊险异常。然彼为戏剧之险，今乃岁首之行，非为驰逐，实欲取吉。环岛中，自念曰：“转八圈还是九圈呼？”八者，立方数也，象体积之张，若气之外扩；九者，平方数也，方整对称，象平面之定，如阵之稳固。八近乎“发”，世俗所喜；九寓乎“久”，古称至尊。余思己身迁异域，事业方启，与其骤发，不若长久。且环岛者，平面圆周运动也，以平方数应之，尤为相称。于是周行九匝，徐徐而出。非为迷信，乃以数理寄意；非求暴起，乃愿恒常。后思之，此举虽微，而心有所托。昔人绕城门以纳福，今我环凯旋而自勉。

曹刿论战

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曹刿论战 先秦• 左丘明今年春，金毛伐波斯，霍尔木兹海峡闭。油船不通，商旅断绝，市价腾踊，金毛国王大惧，朝夕不宁。群臣进曰：“宜急击之！”或曰：“宜和之！”议纷纷而莫决。曹刿闻之曰：“肉食者鄙”，入见。王曰：“海峡既封，奈何？”对曰：“未可知也。”王曰：“彼既封我路，我将何以通？”曹刿不对，乃徐出一册，拂尘而启之，曰：“臣尝读此书。”王视之，乃初中代数也。曹刿指其间一式曰：“负负得正。”王愕然曰：“此何兵法？”对曰：“封者，负也。一负则闭；再负相乘，则正。今彼封之，一负也；王若亦封之，再负也。两负既成，其势自正，是谓‘封封得开’也。”王大悦曰：“善！”遂命左右曰：“传令——亦封之！”既而两国皆曰“封”，封声震海，舟人愈惧。然未几，海峡忽开，商船复通，油气如流，四海皆惊。王喜，问曹刿曰：“此何术也？”曹刿对曰：“臣亦未测，但知算术不欺人耳。”群臣相顾愕然，有人私语曰：“此非用兵，乃用书也。曹刿退而笑曰：“世人但争一负，不知两负；若尽习代数，则天下之事，不惧也。

灰侯

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昔有异兔，号曰“灰侯”，体重十斤有余，毛色斑驳，状若山精。栖于核之禁地，草丰而人寡，因自号“园主”，踞草为王。 其地也，高压围墙，二丈有半，若城若关；又有带刀侍卫巡逻，昼夜不息。凡人至此，望墙而叹，闻卫而却。然灰侯独来独往，行若无人，或伏阴影，或临草坡，摇首摆尾，颇有将相之风。众人相顾曰：“此兔何术而入？” 或曰：“灰侯习遁地之法，夜半潜行，凿地为穴，如龙蛇行，直通园内。”或曰：“非也，彼察墙脚之微隙，拱土而入，一孔之地，胜于千门！”又有善谈者拍案曰：“皆非也！此兔深谙时机之术。门启之际，车来人往，彼乃潜形匿迹，一跃而入，此乃‘借门而遁’之计也。” 更有老者抚须笑曰：“汝等皆未窥其全也。此兔或本居斯地，园未成时，已为此间旧主。及人筑高墙，列强卫，不过据其土耳。兔乃从容不去，反据新园，遂成今日之势。” 众皆默然，复观其行。见灰侯依灌木之侧，处阴阳之交，耳竖如戟，目光流转。外似闲适，内实警惕，一有风吹草动，即可电掣而去。乃知其非愚也，实为“谨慎之勇”。 于是有文士叹曰：“高墙可以御人，不能尽御群灵；重兵可以防盗，未必识得细踪。 灰侯非破阵之雄，亦非掘隧之才，不过识隙而入，因地而安。今草丰而无人争，遂得养尊处优，名震园区。” ​

射箭

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夫射者，非独胆挽强之技，实修身养气之道也。古之君子，六艺并习，而射居其一。故《礼》曰：“射以观德。”盖其所中者，不独皮侯，亦在人心焉。世人多好驰逐，争快斗强，独射者反是。其道贵静，其功在缓。缓而后稳，稳而后准，准而后神。​夫射之有靶，犹射频之有 Smith 圆图也。众线纷纭，终归一心；万点散布，所求惟中。射者执弓而望红心，犹工程师凝目于圆图之中央。盖其中心者，非徒图形之中，实“匹配”之境也。偏于上，则感性渐生；偏于下，则容性已起。稍失其中，则反射暗增，功率空耗；箭若离心，则力虽尽发，终不中的。故调谐之际，如射者调息：或微移电容，若轻转弓臂；或细调相位，如缓定呼吸。虽改动仅毫厘，而驻波顿减；正如箭道既正，百步穿杨。

Usefull command

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This page sumarizes some usefull command. rundll32 sysdm.cpl,EditEnvironmentVariablesEvery Windows account has its own user environment variables, which do not require administrator privileges. You can safely add directories to your user PATH without touching system-wide settings. document.getElementsByClassName(“entry-meta”)[1].style.display=’none’;document.getElementById(“comments”).style.display=’none’;document.getElementById(“site-navigation”).style.display=’none’;document.getElementById(“masthead”).style.display=’none’;document.getElementsByClassName(“site-footer”)[0].style.display=’none’;document.getElementsByClassName(“entry-meta”)[0].style.display=’none’;

Guiding Center Approximation

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The equation of motion used in the particle tracker is based on the Guiding Center Approximation. In a strong magnetic field, a charged particle spirals (gyrates) rapidly around a magnetic field line. Computing the full spiral is computationally expensive and often unnecessary. Instead, we track the Guiding Center—the center point of that spiral. Here is … Read more

Newtonian mechanics and Hamiltonian mechanics

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To find the trajectory of a ball thrown with an initial speed $v_0$ at an angle $\theta$ (projectile motion), we will set up our coordinate system where $x$ is the horizontal distance and $y$ is the vertical height. we consider a particle of mass $m$ in a uniform gravitational field $\mathbf{g} = -g\hat{\mathbf{j}}$. The motion … Read more

The Dance of the Electron Demystifying Magnetic Resonance in Plasma

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One of the most confusing barriers in electromagnetics and plasma physics is the concept of permittivity in a magnetized plasma. Students are introduced to the Stix parameters (like $R$, $L$, and $S$) and told that permittivity can be infinite or even negative. We are shown equations where a singularity appears at the cyclotron frequency ($\omega_{ce}$). … Read more

 from QWERTY to AZERTY French Typing Trainer

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If you are learning French, you know that the grammar is hard. But do you know what’s even harder? Typing. As a lifelong QWERTY user, switching my keyboard layout to French (AZERTY) felt like trying to write with my left hand while blindfolded. I would try to type “qui” and end up typing “auj”. I would reach for a … Read more